When a mechanical assembly is taken apart for inspection or repair, cotter pins holding elements of the assembly are often thrown away and replaced. One reason for this practice is to avoid using cotter pins that are fatigued through repeated plastic bending that may sometimes be necessary to properly secure the cotter pins during periodic inspections or repairs.
I solve the above problem via a cotter pin that is a strong, flexible spring that need not be plastically deformed to secure it to a mechanical element. A slider key riding on the cotter pin's legs forces the legs together before these legs enter a hole. The slider key first slides along the legs toward their diverging, free ends to close the legs toward one another. Then the key pivots on the legs to close them together more completely. The key is of simple, inexpensive construction and can act as a lever to help generate the force to squeeze the pin's legs together.